The present invention relates to an hydraulic valve, which inter alia, can be used as a completely novel type of blocking valve or so-called locking-valve. Such valves find use in hydraulic systems and are intended to block hydraulic lines passing to and from hydraulic motors. Such valves may also be used for the primary purpose of eliminating so-called load creep, which occurs in various types of hydraulic piston-cylinder devices or rams when under load and which, more specifically, means that any load whatsoever held by an hydraulic piston-cylinder device will be slowly lowered due to internal leakage of hydraulic medium in the hydraulic system, and particularly in operating valves present in the system.
Various valves which are intended to prevent load sink are known to the art. The use of pilot-controlled check valves is particularly known in this regard, but these valves have the drawback of being of the on/off-type, i.e. the valve body, or valve plug, of such valves can eityher take solely a fully open posiiton or a fully closed position. This is because the valve body is spring-biased in the direction of its closed position and can only be moved to its open position by a force which exceeds the spring force.
The novel type of valve to which the present invention also relates is based on the principally known technique of controlling or positionally adjusting the valve body independently or pressure, but in dependence on a pilot flow which derives from the main flow controlled by the valve, e.g. blocked.
Such hydraulic valves have the form of seat valves and, compared with conventional pressure-controlled seat valves, have been found to possess many advantages, not least because such valves, as distinct from the pressure-control valves can be set precisely to any position whatsoever between their two limit positions, i.e. between their fully open and fully closed positions, and thereby enable both large and small fluid flows to be controlled continuously with precision, as well as flows which are under pressures greater than 500 bar, without requiring the application of excessively large valve-setting forces. This latter advantage also renders this type of valve particularly useful in systems in which very high pressures occur, for instance in mobile hydraulic systems. Furthermore, because the valve-setting forces are so small, such valves can be remotely controlled with the aid of electric signals or impulses, in a very ready and simple fashion.
This new type of valve, however, also has a number of drawbacks. One primary drawback is that the operating funciton of such valves requires the provision of a valve body which is technically complicated from the aspect of manufacture. This prevents such valves from being fitted with known valve plugs that are capable of being manufactured in large numbers, or which are already available commercially in large numbers, such as spherical balls for instance. Consequently, this type of valve is more difficult and more expensive to use. Furthermore, this type of valve requires a relatively long valve body, which means that the valve itself is also relatively long and cannot be made as compact as would be desired, not least from the aspect of installation.